To increase the productivity of agricultural products, it is necessary to appropriately assess the fertility of the soil. Indexes that indicate the fertility of the soil include the soil fertility characteristics such as available nitrogen, available phosphoric acid, total phosphorus, total carbon, total nitrogen, K, Ca, Mg, Fe, Al, Na, CN ratio, and CEC (cation exchange capacity). To analyze the amount of available nitrogen, for example, methods of subjecting an organic liquid extracted from soil using a phosphate buffer solution to a visible absorption spectrophotometry or an ultraviolet absorption spectrophotometry, and using a near infrared reflectance spectrophotometry have been proposed. As a method of determining these indexes easily, some of the present inventors have proposed a method of illuminating the excitation light to the soil and analyzing the fluorescence spectrum from the soil, thereby estimating the fertility characteristics of the soil (Patent Literature 1).